Please can help me to understand this equation?

Hi all

I wonder if anyone might be able to explain this equation to me, in regard to the exact steps required to work it out? (For example, do I first multiply 1 by the sample size and then multiply this by the sum of each data point ... etc.). I unfortunately don't understand algebra too well and am not sure what to do.
Effective population size.jpg

How could I work out the equation when provided with the following information?:
In five successive generations, the number of individuals in a population is 100, 200, 100, 150, 50. Find the value of the effective population size.

My problem with doing this is just that I really don't understand the process required (step by step) to work out this equation. What does this equation look like when written in full?

I've had a lot of gaps in my maths education, so really struggle.

Please can anyone help me?

Thank you.

(edited 9 years ago)

Reply 1

SnoochToTheBooch

17

That capital E looking symbol means 'sum over the index i from i=1 to i=n.

So you've got N_1, N_2,..., N_n.

You'd first of all calculate (1/N_1) and (1/N_2) and so on all the way to (1/N_n). Then you add those numbers together. Then you divide your total by n. Then you do 1 divided by that number.

Reply 2

Ggdf

OP

6

Original post by SnoochToTheBooch

That capital E looking symbol means 'sum over the index i from i=1 to i=n.

So you've got N_1, N_2,..., N_n.

You'd first of all calculate (1/N_1) and (1/N_2) and so on all the way to (1/N_n). Then you add those numbers together. Then you divide your total by n. Then you do 1 divided by that number.

Thank you very much for explaining to me, I really appreciate it.
How would you represent your total (in terms of letters or symbols) that you divide by n (the stage following adding everything together)?

Reply 3

SnoochToTheBooch

17

Original post by Ggdf

Thank you very much for explaining to me, I really appreciate it.
How would you represent your total (in terms of letters or symbols) that you divide by n (the stage following adding everything together)?

I'm not sure I understand what you're asking - that 'E' symbol part is how you represent that sum?

Please can help me to understand this equation?

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